The staffers deny shadow banning Twitterers, but admit further in their post:

"We do not shadow ban. You are always able to see the tweets from accounts you follow (although you may have to do more work to find them, like go directly to their profile)."

Speaking in plain language, your Tweets can't be seen by anyone on Twitter who doesn't follow you, and they may have to do an unusual amount of work to see your Tweets.

That's shadow banning people by the wikipedia definition:"By making a user's contributions invisible or less prominent to other members of the service, the hope may be that in the absence of reactions to their comments, the problematic or otherwise out-of-favour user will become bored or frustrated and leave the site"

What actions you take on Twitter (e.g. who you follow, who you retweet, etc)

How other accounts interact with you (e.g. who mutes you, who follows you, who retweets you, who blocks you, etc)"

Let's focus on "who mutes you, who follows you, who retweets you, who blocks you, etc" for a moment.

"Decentralizing policy enforcement" in this case puts at least some of the power to shadow ban Twitter accounts in the hands of "who mutes you, who follows you, who retweets you, who blocks you, etc".

Part of the marked discrepancy between conservatives and liberals on Twitter's shadow ban list may be that liberal political organizations famously began using social media on the Internet for organizing of all sorts.

Given the discrepancy exists, and few leftists are so banned, and that the criteria for shadow banning have been set forth by Twitter, it's not unreasonable to suspect that the algorithms Twitter uses to decide who gets a shadow ban are being gamed. You wouldn't have to have many followers to block or mute everyone on a list you draw up to get the algorithm anyone you don't like.

Such lists exist. I'm on two of them, curated by Marethyu (@scathachultor), helpfully labeled "Scum" and "Propagandists/Liars". Given his apparent social skills, it's perhaps unsurprising Marethyu only has 92 followers.

The question, I guess, is how many blocks or mutes do you have to have to get shadow banned on Twitter? Twitter won't say.